1. Field of the Invention
The present invention relates to an oil path structure of an operation hydraulic circuit to control an operation oil pressure in a variable valve timing mechanism of an engine, in particular, an oil path structure in which an oil filter is provided between an oil control valve and an actuator.
2. Description of Related Art Conventionally, a variable valve timing mechanism which varies an opening-closing timing of a suction-exhaust valve by shifting a rotating phase of a camshaft to a rotation of a crankshaft is employed in an engine. In general, in an engine having a variable valve timing mechanism an actuator 3 makes a rotation of the camshaft 2 shift relative to a rotation of the crankshaft 1 by an oil control valve 4 that controls the suction and exhaust of an operation oil of the actuator 3 such as shown in FIGS. 10 to 12. Such an actuator 3 and oil control valve 4 are in communication with each other by an advance-angle side oil path 5 and a delay-angle side oil path 6 as shown in FIG. 3. The actuator 3 is operated on the advance-angle side by moving the oil control valve 4 and being loaded with operation oil in the advance-angle oil path 5, and on the delay-angle side by being loaded with operation oil in the delay-angle oil path 6. Furthermore, the oil control valve 4 is provided with a solenoid 8 which is operated based on a control signal of an ECU (electronic control unit) 7 as shown in FIGS. 4 and 5. The oil control valve 4 varies a valve timing by controlling the suction-exhaust of the operation oil in the actuator 3 by sliding spool 4b in housing 4a in response to the solenoid 8 in such a manner that the rotating phase of the camshaft 2 is shifted in relation to the rotation of the crankshaft 1. In such an actuator 3 of the variable valve timing mechanism, a housing 10 rotates integrally with a camshaft timing sprocket 9; and vanes 11, rotatable around a rotation shaft of the camshaft sprocket 9, rotates within a given range relative to the housing 10. To operate the actuator 3 on the advance-angle side, a spool 4b of oil control valve 4 is moved right-like in FIG. 6 from an intermediate position of FIG. 6 to cause a supply port 12 of the operation hydraulic oil to be communicated with the advance-angle side port 13 and a drain port 15 is made to be communicated with the delay-angle side port 14. Thereby, as shown in FIGS. 4 and 5, the operation oil pressure is loaded on the advance-angle side oil pressure chamber 16 of the actuator 3, and an oil filled in a backward-side pressure chamber 17 is returned to the oil control valve 4 and exhausted from the drain port 15. As a result, the vanes 11 are turned to the advance-angle side relative to the housing 10, that is to the camshaft timing sprocket 9, thereby, the valve timing can be shifted to the advance-angle side. For reference, the operation oil of the variable valve timing mechanism is sucked from oil reserved in an oil pan 18 by an oil pump 19, filtered through an oil filter 22, and pressurized and transmitted to the oil control valve 4 through a branching oil path 20 and oil path 21 as shown in FIGS. 4 and 5.
Further, in such an oil control valve 4a spool 4b fits slidably in a spool hole 4c. The spool 4b is a precisely worked part, so that, if any foreign matter in the operation oil becomes engaged between the spool 4b and the spool hole 4c, the operation of the oil control valve 4 may malfunction. Japanese Utility Model laid-open No. Hei 7-42402 discloses an oil filter for operation oil removable through an opening provided outside an engine is provided in the oil path 21 upstream of the oil control valve 4.
However, in the invention disclosed in the above UM Model laid-open No. Hei 7-42402, it is impossible to remove some foreign matters mixed in the operation oil which is returned to the oil control valve 4 from the actuator 3. As a result, such foreign matters can become engaged with between the spool 4b and the spool hole 4c, and thereby risk causing a malfunction of the oil control valve 4. Further, this oil filter is disclosed disposed at an intersection between perpendicularly crossed oil paths where the operation oil flows inward from a cylindrical opening and flows outward from a side, with the result that a loss of pressure is great, so that, a functional (response function) decrease of the variable valve timing mechanism is problematic.
Therefore, the present invention has been made in the light of the above circumstance, an object of the present invention is to provide an oil path structure in which the operation of the variable timing mechanism is stabilized by providing an oil filter at the downstream of the oil control valve and removing any foreign matter in the operation oil existing between the oil control valve and the actuator.
In order to attain the above object, according to a first aspect of the present invention, an oil path structure for lubricant of an engine in a branching path where a variable valve timing mechanism controls supply and exhaust of oil in an operational oil pressure circuit, comprises an oil filter provided downstream of the oil control valve and extending axially in the direction of an oil path.
By being structured like the above, any foreign matter existing in the operation oil can be removed. Since the oil filter is set while extending in an axial direction, a diameter of the filter can be reduced.
Further, according to a second aspect of the present invention, disposed between the oil control valve and the actuator of the variable timing mechanism are an advance-angle side oil path to operate the actuator to a advance-angle side by being loaded with the operation oil pressure, a delay-angle side oil path to operate the actuator to a delay-angle side by being loaded with the operation oil pressure, and an oil filter set in at least on one of the advance-angle side oil path and the delay-angle side oil path.
By being structured like the above, any foreign matter possibly existing in the operation oil at the downstream of the oil control valve can be removed.
According to a third aspect of the present invention, an oil filter is positioned with its side to a portion where actuator 3 and oil control path are crossed.
By being structured like the above, a pressure loss at the time of passing of the operation oil through the oil filter is extremely reduced.
According to a fourth aspect of the present invention, an oil filter is set in such a manner as it is extended upward linearly from the oil control valve mounting face.
By being structured like the above, foreign matters captured through an oil filter or deposited in a hole set with the oil filter are easily removed. Further, since the area of a filter through which the operation oil passes can be made large, the filter is not likely to become clogged and thus a maintenance cycle of the filter can be set longer.
According to a fifth aspect of the present invention, an oil filter is provided with a sleeve, and its side is formed of a bottomed cylinder of mesh which is fit with the oil path to be formed.
By being structured like the above, the structure of the oil filter can be simplified. Further, since an occupied volume of an oil filter can be set small, an oil filter can be set in the operation oil path for both of the advance-angle side oil path and the delay-angle side oil path.